JPH0697053A - X-ray mask provided with transparent silicon thin film and its manufacture - Google Patents

Abstract

PURPOSE: To minimize the allowable limit of alignment and to enhance lithography efficiency by a simple marking and etching technique. CONSTITUTION: A substrate 23 of anisotropic etching material is provided (a), the first surface of the substrate is masked by a film 33e of pattern material which forms a non-doping area 63 (b), a transparent continuous film 33c is formed against the doping surface (c), a thin film 44 is left by etching the second surface of the substrate, an alignment hole is formed on the non-doping area 63 (d), and an alignment window is formed using the alignment hole and the continuous film.

Description

Detailed Description of the Invention

[0001]

FIELD OF THE INVENTION This invention relates to X-ray lithography, and more particularly to an X-ray mask and method of making the same that includes an in-field photoalignment feature through window means located within the X-ray absorber pattern area of the mask.

[0002]

BACKGROUND OF THE INVENTION A significant amount of the prior art in this field is in the field of lithographic masks, and in particular in the field of X-ray lithography for materials and methods of achieving mask alignment. For example, the paper "Mask Alignment for Manufacturing Integrated Circuits Using X-Ray Lithography" by Jay H. McCoy and P.A. Sullivan provides a general analysis of the major technical problems of X-ray lithography, Alignment plates are being considered in the context of Mylar substrates, external oxide windows, and external X-ray detection schemes. However, it does not propose in-field alignment using a thin film mask.

Another method is the IBM TDB Vol. 20, No. Three
On pages 1187-8, the X-ray fluorescing method was used for the device wafer and mask grill to be irradiated, which emitted the highest emission when the two were exactly superposed. "Masks for Wafer Alignment Systems" by others (IBM TDB
Vol. 16, No. 4, 1306, Sep. 1973
Moon) similarly proposes the use of X-rays with fluorescent materials to achieve alignment. However, here again, no consideration is given to optical alignment.

US Pat. No. 4,868,093, "Device Manufacturing by X-Ray Lithography Using Stable Boron Nitride Mask," issued to R. A. Levy, the boron nitride thin film is optically transparent. Therefore, it can be used for on-board or in-field alignment.

However, although boron nitride thin films can actually be made transparent, they also tend to deform and discolor, apparently losing their transparency when exposed to X-rays. Therefore, the current technology is dominated by silicon thin films.

D. Sparse and H. E. Smith's paper "X-ray Lithography-A New High Resolution Copy Process" (Solid State Technology, July 1972) is a basic paper on the use of X-ray masks based on silicon thin films. .

The alignment plan discussed here and a subsequent paper by H. E. Smith et al., "X-ray Lithography: Complementary Technology to Electron Beam Lithography" (J.
Vac.Sci.Technol., Vol.10, No.6, November / December 1973) uses an X-ray detector to perform accurate alignment based on X-rays radiated through a mask and a wafer ( (Fig. 9)
I am trying. The holes are formed in the device wafer,
No proposals have been made to achieve pattern alignment by optical alignment through the mask.

The German patent "Roentgen Lithography Mask" to the Licensee patent proposes to provide a transparent conductive layer on the silicon thin film before placing the X-ray absorber (gold) pattern for photo-registration. .
The transparent conductive layer is a mixture of indium oxide and tin oxide.

It also acts as a non-reflective coating. Since the light passes through the area without the gold absorber, that area can be used for light alignment. This patent specifically describes plates of plated substrates. This is usually a thin layer of gold-chromium or titanium with an opaque track, deposited in front of the gold absorber.

Currently, this thin layer is easily removed by ion beam etching in the unplated areas, which is not a problem. However, the proposal that photo-alignment is possible because the substrate layer on top of the silicon film is transparent ignores the fact that the silicon film itself is not sufficiently transparent for precise photo-alignment. .

Japanese Patent No. 58-19952 to Hitachi
5 (A) "Mask to X-Rays" discloses a process performed by pre-etching a plated substrate in a mask area to define an alignment mask of the same material (obviously polysilicon) rather than gold as the mask. ing. Neither this patent nor the aforesaid German patent suggest any removal of the mask substrate material to enhance the light irradiation.

The use of holes for masks is disclosed in German Patent No. 3232498 to Phillips, "Titanium Mask for X-Ray Lithography", which includes an X-ray mask with a thin film of titanium metal. The holes in the thin film are covered with polyimide plastic and act as alignment marks for optical alignment. The alignment according to this proposal is the same external alignment as the current method with a silicon mask.

US Pat. No. 4,176,281 to P. Tisher et al., "Method of Adjusting a Semiconductor Disk for a Radiation Mask in X-Ray Photolithography," describes X-rays using hole alignment through both the mask and the device wafer. Whereas the detection method has started,
U.S. Pat. No. 4,513,203, "Masks and Systems for Aligning Objects of an Exposure System to Each Other," to Boren et al., Describes using both electron beams and holes through thin films for alignment. ing. But,
Neither of them proposes that the position of the alignment hole pattern and the optical alignment be outside the actual mask area, ie outside alignment.

US Pat. No. 4,855,197, "Mask for Ion, Electron, or X-Ray Lithography and Method of Forming It," to W. Zapka et al. Deals with the distortion of silicon thin films that are moved by the incident radiation during lithography. It is based on the planned temperature distributed in the thin film,
It proposes a method to reduce or eliminate the strain by adjusting the doping profile of the thin film.

US Pat. No. 4,88 to Kay Hosono
No. 7,283 “X-ray mask and exposure by a method using an X-ray mask” also deals with the mask distortion, and mechanically “bends” the frame supporting the X-ray absorber pattern, thereby eliminating the distortion during exposure. It proposes that it can be modified dynamically.

As described above, although various X-ray masks have been proposed in the prior art, it will be appreciated that all of them have limitations regarding the use of materials and photoalignment.

[0017]

As can be seen from the above description, the prior art currently supports a silicon thin film as a material for an X-ray mask. However, the silicon thin film used as a mask for X-ray lithography has poor transparency and is relatively opaque to visible light.

Performing a conventional mask for the wafer photolithography alignment procedure, (1) having a lithographic alignment pattern for the external surface (separated wafer or substrate), (2) on the thin film portion of the X-ray mask. Achieving high precision photo-registration of lithographic X-ray absorber patterns supported on a substrate is difficult. As such, such alignment is typically performed using an alignment pattern that operates outside the active thin film area containing the lithographic x-ray absorber pattern.

The in-field photo-alignment pattern defined in the lithographic X-ray mask pattern area of the thin film can significantly enhance lithographic performance by this technique by minimizing the alignment tolerances or tolerances. However, there is currently a small possibility that such a technique can be processed.

Accordingly, it is an object of the present invention to have a photo-alignment system formed in a lithographically active thin film area that can be easily manufactured using simple masking and etching techniques that can replace mask preparation. The purpose of this is to provide a silicon X-ray mask which can significantly enhance the lithographic performance by making it possible to minimize the alignment tolerance.

[0021]

The present invention is configured as described below in order to solve the above problems. That is, the present invention provides an X-ray mask (preferably silicon) having an array of microwindows for improved light transmission (or light irradiation) that allows for in-field light alignment within the lithographic patterned area of the mask. Including.
This mask is preferably doped with boron and is made of a silicon wafer or substrate having a thin film portion containing lithographically patterned areas.

By completely removing silicon (Si) from selected areas, a pattern or array of small openings or holes is formed in the thin film portion. The thin film portion is supported so as to be surrounded by a Si substrate, and both surfaces (at least one surface) thereof are coated with a film of a light transparent material.

The combination of holes and film creates a small transparent window or microwindow of Si thin film material that allows almost 100% light transmission therethrough, which window acts as a pattern of photoalignment holes to the mask. I made it possible.

In a preferred manufacturing method of the present invention, one surface of a Si wafer is masked and doped prior to boron doping with a boron diffusion mask material, such as a silicon nitride film, resulting in a thin boron surface of the wafer. A pattern is formed that leaves an array of small undoped areas in the doped P ⁺⁺ layer.

After doping, the mask film is removed and, if desired, a new light transmissive film such as silicon nitride is provided on both sides of the wafer. Therefore,
The mask film on the side of the wafer opposite the boron-doped layer is patterned, followed by anisotropic etching of the substrate against the patterned boron-doped P ⁺⁺ layer on the wafer surface.

The resulting structure is one that has holes in the undoped areas of the boron-doped P ⁺⁺ thin film. An X-ray absorber pattern is then defined on the thin film and the entire wafer is attached to a suitable support ring to complete the X-ray mask structure.

The thin film silicon-free holes covered by the silicon nitride film are, before their exposure to X-rays, due to their geometrical structure and transparency, using another separating member or a co-pattern of the wafer. High precision pattern alignment allows X to be supported on the thin film of the device with respect to a pre-existing device pattern on the separated separate wafer surface.
Form a window or array that allows the line mask absorber pattern to be optically aligned.

A mask with a window located in the x-ray mask absorber pattern area can have on-board or in-field alignment with a small alignment tolerance to provide enhanced alignment accuracy.

[0029]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT A preferred embodiment of the present invention will now be described in detail with reference to the accompanying drawings. FIG. 1 is a cross-sectional view of an X-ray mask substrate constructed according to a preferred embodiment of the present invention. In FIG. 1, 1 is a mask, preferably a wafer or substrate 2 made of a suitable material for an X-ray mask of silicon and an optically transparent film, preferably made of silicon nitride, on opposite sides of the substrate 2. 3a and 3b and film 3a
And a thin film 4 forming a layer adjacent thereto.

Reference numeral 5 is an opening formed in the substrate 2 toward the thin film 4 and forming a structure of an optically unshielded Si thin film coated with a silicon nitride film supported by the surrounding Si substrate 2. is there. Thin film 4 is silicon nitride
It has a group of holes 6 formed so as to form a pattern or array of transparent microwindows with the film 3a.

The microwindow pattern is selected to be geometrically and structurally compatible with an X-ray absorber pattern (not shown) that will be defined later in the thin film area and will act as an X-ray mask. The alignment of the microwindow pattern with the co-pattern of the separated substrate during alignment facilitates the alignment of the external pattern on the surface of the separated substrate or member with the absorbent pattern. You can choose to

The microwindow pattern can be placed in the X-ray mask pattern area for onboard or infield alignment. A suitable support ring 10 completes the X-ray mask structure.

The holes 6 are formed in various shapes and can be arranged in arrays of various geometric structures and densities to accommodate the appropriate alignment system. For example, as can be seen in FIG. 2, the openings can form one or more various arrays such as squares 20, rectangles 22, triangles 24, and crosses 26, etc., and can be arranged in a regular pattern or alignment scheme. It can be configured in a suitable random shape to achieve the desired mask pattern alignment with the separation substrate pattern to be illuminated.

An array of micro-windows of predefined geometrical structure and density increases the average optical transmission in proportion to the regional coverage of the micro-window,
It is formed using a film of a light transparent material such as silicon nitride, silicon dioxide, silicon oxynitride, silicon carbide, boron nitride, aluminum oxide, diamond, etc. (see FIG. 2).

For example, 100 × 100 of a simple 5 μm square silicon nitride microwindow with a center of 10 μm.
The array has 50 mm optical transmission in a 1 mm square area.
It will be increased by%. A 50-100 mm thick silicon nitride film has negligible light absorption and has excellent mechanical, chemical and processing properties. It can be seen that the self-supporting silicon nitride microwindow can be used as a substrate for an electron microscope.

[0036] a to d in FIG. 3 is preferred according to the present invention X
It is a figure which shows the manufacturing method of a line mask. As shown in FIG. 3, in the starting step a , for example, a wafer 23 of lightly doped <100> single crystal Si is deposited on its surface by low pressure chemical vapor deposition (LP-CVD), preferably Has dopant diffusion mask films 33a and 33b which are silicon nitride.

Film 33b is not required for this manufacturing method, but it is conveniently formed by an LP-CVD process, the use of which can result in reduced mechanical strain and tension problems, as will be described below. , Provides a more rigorous finished structure in the form of a three-layer sandwich with silicon nitride coated on both surfaces.

Also, although silicon nitride is used herein as an example of a preferred material for the transparent microwindow, other coating materials such as those mentioned above can also be used to advantage, especially silicon carbide, dioxide. Composite materials and multilayers including silicon, diamond and the like can be used.

In order to start the formation of the microwindow, the film 33b is etched off and the film 3b is removed.
3a has a lithographically defined microwindow pattern 33e ( b 3 in FIG. 3) defined therein for use as a mask for the adjacent surface of the Si wafer. The wafer surface is suitably doped with a dopant that is etch resistant to Si, such as boron, to form an etch resistant layer or thin film 43 on the wafer. Pattern 33e of the silicon nitride film 33a is as seen in b of FIG. 3, leaving a pattern of small non-doped area 63 in the portion 83 of the thin boron-doped P ⁺⁺ layer 43 produced on the wafer surface.

After doping, the patterned mask film 33a is optionally removed (retained if appropriate) and a new light transparent silicon nitride film 33c is formed.
And 33d are attached to both surfaces of the wafer 23 by the LP-CVD method.

A mask film 33d is patterned on the opposite side of the boron-doped pattern-containing layer 43 of the wafer, followed by anisotropic etching of the wafer body or substrate 23 to contain the micro-window pattern of the boron-doped P ⁺⁺ layer 43. The portion 83 is etched ( c in FIG. 3). As can be seen in FIG. 3d , the resulting structure is part 83 of the boron-doped P ⁺⁺ layer 43.
Boron-doped P ⁺⁺ thin film 44 extended over the length of and adapted to receive an X-ray mask absorber pattern
including.

The thin film 44 is surrounded and supported by the Si substrate 23 and has "holes" (pinholes or small openings) 63 etched through its undoped areas. The silicon-free holes 63 of the thin film 44 covered by these silicon nitride films 33c are locally arranged in the X-ray mask pattern area 83 of the thin film 44 when this structure is to function as an X-ray mask.
The transparency and geometric structure creates a pattern of microwindows 73 that can be used for its light and pattern alignment, allowing onboard alignment.

FIG. 4 is an enlarged sectional view of a portion of the thin film 44 showing the two micro windows 73 in detail along the portion of the X-ray absorber pattern 84. Also, FIG. 4 is an external isolation substrate 90 (typically in an x-ray mask application) which is typically a semiconductor wafer having a pre-existing integrated circuit pattern 89 that must be precisely aligned with the x-ray absorber pattern 84. Indicates.

Substrate 90 is a co-registration pattern 91 adapted to be aligned with a microwindow pattern.
Holding two wafers or substrates (23, 90) close to each other for X-ray radiation processing.
4 and the integrated circuit pattern 89 are formed with high precision alignment.

Boron doping and etching procedures for use in proper manufacturing processes are described in "MICROELECTRONIC".
ENGINEERING "(9 (1989) pp. 167-170),
And IBM Technical Bulletin (Vol.33, No.5, 19)
October 1990), both incorporated by reference, by the inventor of the present invention entitled "Boron Doping.
Highly selective KOH ground etchant (or etchant) for silicon structures ".

The microwindow geometry for the x-ray mask is determined by alignment considerations (general and local) as well as by factors related to mechanical strain and tension. As mentioned above, by coating silicon nitride on both sides to form a three layer sandwich,
Rigorous thin film structures can be created. Thus, the complete structure can be formed by coating the silicon nitride on the anisotropic etched side, including the thin film 44 itself, to form the layer 33f shown in dotted lines in FIG.

Moreover, the microwindow array is
When it is formed in an area where boron doping is not done, by carefully masking that area and etching from the opposite side to create a thin film silicon-less “hole” or pinhole, The thin film can be formed without compromising the maintainability. The surface of these thin films is protected by a silicon nitride film that extends continuously over the entire surface of the mask with microwindows formed in the holes or openings in the thin films.

A "hole" or pinhole pattern is
Another patterned wafer, such as a semiconductor substrate, which corresponds to a lithographically defined microwindow alignment pattern on the wafer surface prior to boron doping, and which has an integrated circuit pattern formed therein after a successive etching step or Forming a group of locally positioned transparent alignment holes that can be used to properly orient and align the member and mask.

The hole patterns can have different shapes and include a fiducial mark which will correctly align the co-alignment pattern on the separation substrate to provide precise alignment of the mask and circuit pattern. . The shape of the holes is chosen to maximize light transmission without compromising the mechanical and geometric integrity of the x-ray mask absorber pattern.

The locally transparent microwindow regions thus imparted to the thin film improve the in-field optical alignment of the intended X-ray lithography by minimizing the alignment tolerance and provide the benefits of achieving it. I was able to.

The shape of the array pattern for the microwindow depends on the application parameters such as the size of the X-ray exposure field and the constraints imposed by the X-ray mask absorber pattern, and the design for the alignment tool based on the tool's alignment system algorithm. Depends on matching. There may be many combinations-(and the alignment set approaches the 50 mm total set mark)-appropriate combinations are certainly tools, and software that depends on the particular tool.

Although the present invention has been described in detail with reference to the preferred embodiments thereof, the present invention is not limited thereto, and many changes and modifications can be made within the scope of the idea of the present invention. Will be apparent to those skilled in the art.

[0053]

As described above, according to the present invention, the alignment tolerance can be minimized by a simple masking and etching technique, and the performance of X-ray lithography can be considerably improved. .

[Brief description of drawings]

FIG. 1 is a cross-sectional view of a mask substrate having a thin film illustrating an optically transparent microwindow that is subsequently formed according to a preferred embodiment of the present invention.

2 is a plan view of a mask substrate illustrating various shapes of the group of microwindows or microwindow arrays shown in FIG. 1. FIG.

Figure 3 shows a manufacturing process of forming a transparent micro-windows in accordance with a preferred embodiment of the present invention, a is diagram b showing the step of providing a substrate having a mask film substrate to form a non-doping area Figure c shows the step of providing a mask on the first side and Figure d shows the step of doping the first side of the substrate to form undoped areas. Figure d shows the step of etching the base to form the alignment window. Figure

FIG. 4 is an enlarged cross-sectional view illustrating the alignment of a substrate and thin film detailing a transparent microwindow made in accordance with a preferred embodiment of the present invention with a cooperating external member provided in the use of an x-ray mask.

[Explanation of symbols]

1 Mask 2 Substrate 3a, 3b Film 4 Thin Film 5 Opening 6 Hole (Small Opening) 10 Support Ring 20 Opening (Square) 22 Opening (Rectangular) 23 Wafer 24 Opening (Triangle) 26 Opening (Cross) 33a, 33b Mask Film 33c Silicon nitride film 33d Light absorber 33e Micro window pattern 43 Boron doping P ⁺⁺ layer 44 Thin film 63 Undoped area (Alignment window) 73 Micro window 83 X-ray mask pattern area 84 X-ray absorber pattern 89 integrated circuit pattern 90 separation substrate

 ─────────────────────────────────────────────────── ─── Continuation of the front page (72) Inventor Angela Coco Lambert No. 9 at Gardenia Road, Putnam Valley, New York, USA 10579

Claims (10)

[Claims] 1. A method of manufacturing an X-ray mask having an in-field light alignment function in an area including an X-ray absorber pattern, the anisotropic etching having a first surface and an opposing second surface. Providing a substrate of material, masking the first substrate surface with a film of pattern material to form undoped areas corresponding to a group of alignment holes in the doping of the first surface, An undoped area of the pattern of the set of alignment holes in a doping layer formed on the first surface by doping the first surface of the substrate with a dopant that provides an etch resistance. To form a continuous film of a material that is substantially optically transparent to the surface of the doping layer, and is opposed through the substrate. And anisotropically etching the doping layer from the second surface to form a thin film of the doping layer supported by an X-ray absorber pattern, and a pattern of the group of alignment holes in the thin film. A step of removing substrate material in the undoped area to form an opening, the hole in combination with the continuous film accommodating light passage for in-field light alignment of the x-ray mask. An optical window is formed to form an X-ray mask. 2. The method of manufacturing an X-ray mask according to claim 1, wherein the anisotropic etching material of the substrate is made of silicon. 3. The anisotropic etching material is <100>
The method of manufacturing an X-ray mask according to claim 1, wherein the X-ray mask is made of single crystal photo-doped silicon. 4. The method of claim 1, wherein the doping layer formed on the first surface comprises a thin boron-doped P ⁺⁺ silicon layer. 5. The continuous film of substantially optically transparent material is silicon nitride, silicon dioxide, silicon.
The method of claim 1, wherein the X-ray mask is selected from the group consisting of oxynitride, silicon carbide, boron nitride, aluminum oxide, diamond, and combinations thereof. 6. The method of claim 1, wherein the mask film comprises a boron diffusion barrier material. 7. The manufacture of an X-ray mask according to claim 1, wherein the mask film is composed of multiple layers and composite materials selected from the group consisting of silicon carbide, silicon dioxide, diamond, and combinations thereof. Method. 8. The method of making an X-ray mask comprises the step of removing the mask film from the surface of the doping layer prior to forming the continuous film of substantially optically transparent material. The method of manufacturing an X-ray mask according to claim 1, wherein 9. The method of manufacturing an X-ray mask, comprising the step of supplying a film of a substantially optically transparent material to the surface of the thin film facing the first surface. Item 2. An X-ray mask manufacturing method according to Item 1. 10. An X-ray mask having an in-field light alignment function in an area including an X-ray absorber pattern, the substrate having an opening, the X-ray mask absorber pattern supported by the substrate, and the X-ray mask absorber pattern. A thin film having an area substantially aligned with the opening including a pattern of alignment holes passing through, and, on the thin film, transmitting light through the pattern of the alignment holes arranged on the alignment holes in the area. A substantially optically transparent film to form a light window for passage therethrough, and optically aligning the pattern of the alignment holes with the pattern of the opposing external member to absorb the X-ray mask. An X-ray mask, wherein the agent pattern and the separation pattern of the external member are aligned with each other.